As recording media for recording various types of software such as video data, audio data, or data for computers, recording media such as magnetic disks, optical discs and magneto-optical discs have been popularized.
In recent years, the advancement of the high-efficiency coding technique has enabled band compression of all kinds of data including video data so that these data are handled as digital data. Along with this, increase in capacity of recording media and improvement in recording density are demanded. However, as the recording density of a recording medium is improved, the difference between a signal 1 and a signal 0 read out from the recording medium is reduced, causing decrease of a read margin and hence deterioration in quality of reproduced signals. To avoid such deterioration in quality of reproduced signals, for example, a low-frequency component of a recording signal may be restrained when recording this signal to a recording medium. This is because a signal reproduced from the recording medium includes a large amount of low-frequency noise. However, when this low-frequency is removed by a filter to improve S/N, a necessary low-frequency component for a reproduced signal is cut, too. Thus, a technique of restraining the low-frequency component of the recording signal in advance and thus avoiding its influence, and a data coding system that enables restraint of the low-frequency component are proposed.
However, in some cases, even if this coding system is applied, a long data pattern in which its low-frequency component cannot be restrained may continue. Therefore, scrambling of data is effective for lowering the probability of occurrence of such cases.
Meanwhile, in the case of recording data to a recording medium and reproducing the data, data of a suitably defined size is handled as a unit (hereinafter referred to as sector) and recording and reproduction are carried out using this sector. A code recorded to this sector has its run length limited in order to narrow the frequency bandwidth of communication of the recording and reproducing device. It is known that once an error occurs when recording and reproducing the data of the sector with the limited run length, the error propagates not only to this error part but also to the subsequent data part. In order to prevent this propagation, a predetermined pattern called sync code that can be discriminated from recording data is recorded at a predetermined interval in the sector.
For an optical disc or the like, a scrambling circuit inputs a part of a logical address accompanying input of main data, for example, high-order four bits, as a seed selection signal, and changes scrambled data for each of 16 logical addresses. The scrambled data in this case is one of 16 types of pseudo-random number sequences that are different from one another. Each pseudo-random number sequence is sequentially selected in accordance with the scrambled data for each sector, and data of one sector is scrambled using the selected pseudo-random number sequence.
The scrambling circuit as described above finds exclusive OR of main data and a random number generated from a maximum length sequence expressed by a predetermined generating polynomial, for each bit of both data.
However, in the case a data string to be recorded is text data or the like, a relatively monotonic random data pattern is generated even if the above-described scrambling is performed to generated random data. Such random data has a problem that it lacks error correction capability particularly in high-density recording and therefore lowers the recording/reproducing characteristic.